Photoreduction method for metal complex ions

ABSTRACT

The present invention provides a photoreduction method for metal complex ions by which strict controllability is not required in the control of its exposure amount, and a size of the metallic structure to be produced can be controlled, besides there is no fear of reducing spatial resolution of the size of the metallic structure to be produced. The photoreduction method for metal complex ions wherein a laser beam is beam-irradiated on a metal complex ion dispersion element dispersed in a material to photoreduce the metal complex ions thereby fabricating a metallic structure, includes the steps of adding a predetermined coloring matter to the material in which the metal complex ion dispersion element is dispersed, and beam-irradiating the laser beam to the material to which the predetermined coloring matter has been added.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a photoreduction method for metalcomplex ions, and more particularly to a photoreduction method for metalcomplex ions suitable for use in case of fabricating a metallicstructure by irradiating a laser beam to photoreduce the metal complexions.

2. Description of the Related Art

In recent years, ultramicrofabrication technology such as opticallithography technology, and optical disk manufacturing technologywherein a light is applied is widely utilized, and such technology hasbeen studied in a variety of fields.

For instance, the most widely applied ultramicrofabrication technologyat present wherein a light is applied is the above-described opticallithography technology. The optical lithography technology is a backbonetechnology for manufacturing a variety of electronic devices such as asemiconductor chip. The technology relates to a massive copyingtechnology applying a photo-transferring technology in principle whereina metal in a specified region is dissolved, deposited, or removedfinally in a chemical manner, whereby a desired metallic pattern isfabricated as a metallic structure.

On one hand, a manner for fabricating a metallic pattern by irradiatingdirectly a laser beam on a specified material is known as a technologyfor fabricating a desired metallic pattern as a metallic structure otherthan the above-described optical lithography. More specifically, therehave been proposed a manner wherein a laser beam is beam-irradiated on adispersion element made of metallic nanoparticles, whereby the metallicnanoparticles are molten and bound at the intermediate focus point ofthe laser beam applied, so that a metallic pattern is fabricated as ametallic structure; a manner wherein a laser beam is beam-irradiated onmetal complex ions, so that the metal complex ions are photoreduced todeposit a metallic body, whereby a metallic pattern is fabricated as ametallic structure, and the like manners.

In the above-described manner wherein the metallic body is deposited byphotoreducing the metal complex ions, when the laser beam is scannedwhile beam-irradiating the metal complex ions, it is possible tofabricate an arbitrary metallic pattern in response to the locus scannedas a metallic structure. Accordingly, its applicable range is extremelywide, so that studies and developments are made upon the manner in avariety of fields in recent years.

The inventor of this application has made on a study as to a mannerwherein a multiphoton absorption process using an optical system inwhich a femtosecond ultrashort pulse laser is applied among lasers as alight source is utilized, whereby metal complex ions are photoreduced,so that the metal complex ions are photoreduced at only the intermediatefocus point of the laser beam in a three-dimensional space, and athree-dimensional metallic structure is directly fabricated.

In the meantime, a technology wherein a laser beam is beam-irradiated onmetal complex ions to photoreduce the metal complex ions thereby tofabricate a metallic structure involves such a problem that a control ofthe light exposure is difficult.

One of the major causes of a difficulty in controlling the lightexposure is in that a metal deposited as a result of photoreduction ofthe metal complex ions causes the absorption spectrum or the absorptionsectional area of the material itself to change, so that characteristicproperties of the material which is subjected to laser beam irradiationchange momentarily as a result of the laser beam irradiation. In otherwords, in case of irradiating a light on a material, a constant exposurepattern cannot be maintained so far as such control that opticalintensity of the light to be irradiated following to the precedentirradiation is allowed to change timely in response to an amount of thelight which has been exposed until then is executed strictly. However,it has been extremely difficult usually to execute such strict controlof the optical intensity.

Furthermore, in the case when a laser beam is beam-irradiated tophotoreduce metal complex ions to fabricate a metallic structure, anabsorption factor of light increases usually with deposition of ametallic structure. In these circumstances, there are many cases wherethe reaction proceeds explosively just at the moment when an increasedamount of the metallic structure exceeds a certain threshold value.Thus, there is such a problem that it is difficult to control a size ofthe metallic structure produced.

Particularly, when the above-described explosive reaction begins, thephotoreduction of metal complex ions existing in the vicinities of theintermediate focus point of a laser beam proceeds at the same time.Hence, there is also such a problem that a metallic structure producedbecomes extremely large as compared with a size of the intermediatefocus point of a laser beam, whereby its spatial resolution decreases.

OBJECT AND SUMMARY OF THE INVENTION

The present invention has been made in view of the above-describedvarious problems involved in the prior art, and an object of theinvention is to provide a photoreduction method for metal complex ionsby which no strict controllability is required in control of an exposureamount, besides a size of a metallic structure produced can becontrolled, and further there is no fear of decreasing spatialresolution of the size of the metallic structure produced.

In order to achieve the above-described object, a photoreduction methodfor metal complex ions according to the present invention is the onewherein a laser beam is beam-irradiated on a metal complex iondispersion element dispersed in a material such as a liquid, vapor, anda solid to photoreduce the metal complex ions thereby fabricating ametallic structure, including the step of adding a predeterminedcoloring matter to the material in which the metal complex iondispersion element is dispersed, whereby photoreduction of the metalcomplex ions is controlled to improve a process tolerance in case offabricating the metallic structure. As a result, for example, it becomespossible to directly manufacture a three-dimensional metallic structurehaving a nanomicron size.

More specifically, in the photoreduction method for the metal complexions according to the present invention, a specified coloring matter isadded to a metal complex ion dispersion element, whereby an absorptionspectrum and an absorption sectional area of a non-processed materialare maintained at constant, and it is prevented to propagate energy ofthe laser beam to an area other than the intermediate focus point of thelaser beam, besides photoreduction efficiency at the intermediate focuspoint of the laser beam is improved.

Namely, the present invention may be a photoreduction method for metalcomplex ions wherein a laser beam is beam-irradiated on a metal complexion dispersion element dispersed in a material to photoreduce the metalcomplex ions thereby fabricating a metallic structure, comprises thesteps of adding a predetermined coloring matter to the material in whichthe metal complex ion dispersion element is dispersed; andbeam-irradiating the laser beam to the material to which thepredetermined coloring matter has been added.

Furthermore, the present invention may be the photoreduction method formetal complex ions wherein the coloring matter has the peak ofabsorption wavelength in the vicinity of about half of the wavelength ofthe laser beam which is beam-irradiated to the material.

Moreover, the present invention may be the photoreduction method formetal complex ions wherein the functional groups of the coloring matterhave not a reducing ability with respect to the metal complex iondispersion element dispersed into the material.

Still further, the present invention may be the photoreduction methodfor metal complex ions wherein the material is Au⁺ aqueous solution; thecoloring matter is any of P-Quaterphenyl, Stilbene 420, Coumarin 440,Coumarin 481, Coumarin 485, Coumarin 500, or Coumarin 515; and asolution prepared by dissolving the coloring matter into adimethylformamide solvent is added to the Au⁺ aqueous solution.

Yet further, the present invention may be the photoreduction method formetal complex ions wherein a concentration of the coloring matter is 0.1wt % with respect to the dimethylformamide solvent.

Besides, the present invention may be the photoreduction method formetal complex ions wherein the material is Ag⁺ aqueous solution; thecoloring matter is any of Stilbene 420, Coumarin 440, Coumarin 504, orCoumarin 515; and a solution prepared by dissolving the coloring matterinto an ethanol solvent is added to the Ag⁺ aqueous solution.

In addition, the present invention may be the photoreduction method formetal complex ions wherein a concentration of the coloring matter is setout at the amount of saturation with respect to the ethanol solvent.

Since the present invention is constituted as mentioned above, it mayprovide such excellent advantageous effects that strict controllabilityis not required in the control of its exposure amount, and a size of themetallic structure to be produced may be controlled, besides there is nofear of reducing spatial resolution of the size of the metallicstructure to be produced.

The method of the present invention as described above may be applied tooptical memory technology, optical processing technology, UV lightmolding technology, or optical lithography technology. Accordingly, thepresent invention may be applied to manufacturing of optical disks,laser processing equipment, optical molding equipment or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 is a schematic constructional explanatory view showing an opticalsystem used for experiments by the inventor of this application;

FIG. 2 is an electron micrograph showing experimental results made bythe inventor of this application;

FIG. 3 is an electron micrograph showing experimental results made bythe inventor of this application;

FIG. 4 is an optical micrograph showing experimental results made by theinventor of this application; and

FIG. 5 is an optical micrograph showing experimental results made by theinventor of this application.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, an example of a manner of practice of thephotoreduction method for metal complex ions according to the presentinvention will be described in detail by referring to the accompanyingdrawings.

The photoreduction method for metal complex ions according to thepresent invention is executed in such that a coloring matter having apredetermined absorption wavelength and absorption sectional area whichis in such form that the coloring matter is dissolved in a predeterminedsolvent (for example, water or an organic solvent) is added to amaterial in which a metal complex ion dispersion element has beendispersed, and then a laser beam is beam-irradiated to the resultingproduct.

As an effective coloring matter in case of photoreducing metal complexions by the use of two-photon absorption process by means of irradiationof a laser beam such as a femtosecond ultrashort pulse laser, thecoloring matter the absorption wavelength of which has the peak in thevicinities of about half of the laser beam to be beam-irradiated to amaterial; and the absorption end on the long wavelength side expands upto substantially red zone, in other words, there is no absorption innear-infrared zone is preferred. For example, when a wavelength of alaser beam to be beam-irradiated to a material has a wavelength ofaround 800 nm, a coloring matter the absorption wavelength of which hasthe peak in the vicinities of a wavelength of 350 to 450 nm; and theabsorption end on the long wavelength side expands up to substantiallyred zone, in other words, there is no absorption in near-infrared zoneis preferred.

Furthermore, concerning luminous efficacy of a coloring matter, when thecoloring matter having high luminous efficacy is added to a material, anaction for suppressing absorption characteristics of the material can beobtained, while a coloring matter having low luminous efficacy is addedto a material, an action for elevating absorption characteristics of thematerial may be obtained. This is because the coloring matter havinghigh luminous efficacy absorbs once incident radiation energy, and then,the most of the incident radiation energy is consumed as fluorescence,so that photoreduction of metal complex ions is obstructed. On the otherhand, the coloring matter having low luminous efficacy allows theincident radiation energy absorbed to transit directly to metal ions,whereby either metal complex ions are caused to be reduced, ordischarged as heat, and then the heat energy is again absorbed by metalions. As a result, the metal complex ions are reduced. Accordingly, whena coloring matter of low luminous efficacy is added to a material, areduction efficiency of the metal complex ions is improved by a quantitycorresponding to that wherein an absorption amount of light increases asa result of adding a coloring matter.

Moreover, when a coloring matter is selected, such coloring matterwherein a functional group itself in an coloring matter molecule has noreducing ability with respect to metal complex ions is to be selected.This is because when the coloring matter itself reduces the metalcomplex ions, the metal complex ions in the material are reduced, sothat an intended metallic structure cannot be fabricated.

As a result of studying experimentally coloring matters, it has beenfound that a gold structure can be manufactured by beam-irradiating alaser beam on an Au⁺ aqueous solution being a material prepared byadding the following coloring matters to dimethylformamide solventwithout requiring strict controllability in the control of an exposureamount while controlling a size of the resulting gold structure withoutdecreasing the spatial resolution. The Au⁺ aqueous solution is preparedby adding a coloring matter such as p-Quaterphenyl, Stilbene 420,Coumarin 440, Coumarin 481, Coumarin 485, Coumarin 500, or Coumarin 515which has been dissolved into the above-described dimethylformamide(DMF) solvent to the Au⁺ aqueous solution (for example, an aqueoussolution of HAuCl₄) as a material containing a metal complex ion elementin the case where gold ions are photoreduced as the metal complex ions.

Furthermore, it has been found that a silver structure can bemanufactured by beam-irradiating a laser beam on an Ag⁺ aqueous solutionbeing a material prepared by adding the following coloring matters toethanol solvent without requiring strict controllability in the controlof an exposure amount while controlling a size of the resulting silverstructure without decreasing the spatial resolution. The Ag⁺ aqueoussolution is prepared by adding a coloring matter such as Stilbene 420,Coumarin 440, Coumarin 504, or Coumarin 515 which has been dissolvedinto the above-described ethanol solvent to the Ag⁺ aqueous solution(for example, an aqueous solution of AgNO₃) as a material containing ametal complex ion element in the case where silver ions are photoreducedas the metal complex ions.

Concerning a concentration of a coloring matter, when dimethylformamideis used as a solvent and an amount of a coloring matter is made to be0.1 wt % or less (a concentration of the coloring matter with respect tothe dimethylformamide solvent), reduction of gold ions due to additionof the coloring matter is not observed. Moreover, when the invention iscompared with the prior art, improvements are observed in resolution ora surface condition of the gold structure fabricated in thephotoreduction by means of a laser beam.

On one hand, in the case where silver ions are photoreduced as theabove-described metal complex ions, ethanol may be used as a solvent;and a concentration of a coloring matter may be set out to the amount ofsaturation. The amount of saturation changes dependent upon a coloringmatter. For instance, it is 0.01 wt % (the concentration of the coloringmatter with respect to an ethanol solvent) in case of Stilbene 420, itis 0.02 wt % (the concentration of the coloring matter with respect toan ethanol solvent) in case of Coumarin 440, itis 0.08 wt % (theconcentration of the coloring matter with respect to an ethanol solvent)in case of Coumarin 504, and it is 0.02 wt % (the concentration of thecoloring matter with respect to an ethanol solvent) in case of Coumarin515. When a concentration of a coloring matter is set out to its amountof saturation, improvements are observed in resolution and a surfacecondition of the silver structure fabricated in photoreduction by meansof a laser beam in the invention as compared with the prior art. On theother hand, no reduction of silver ions due to addition of a coloringmatter is observed.

The experiments by which the above-described results are obtained andwhich are made by the inventor of this application will be describedhereinbelow as examples 1 to 2.

In the experiments shown as examples 1 to 2, an optical system 10 shownin FIG. 1 is used. The optical system 10 is composed of atitanium-sapphire laser 12 as a femtosecond ultrashort pulse laser, acondenser lens 14 for condensing the laser beam output from thetitanium-sapphire laser 12, and an XYZ stage 18 for supporting atransparent glass substrate 16 with respect to the laser beam outputfrom the titanium-sapphire laser 12 and further being transferablefreely in an X-axis, a Y-axis, and a Z-axis directions (see thereference drawing corresponding to FIG. 1 showing the XYZ-orthogonalcoordinate system).

It is to be noted that the titanium-sapphire laser 12 has 800 nm centralwavelength λ, 80 fs pulse width Δt, and 80 MHz repetition frequency f,respectively.

Moreover, on the substrate 16, a material containing a metal complex iondispersion element, and a material containing a metal complex iondispersion element added in such form that a coloring matter isdissolved in a solvent are placed as a sample S.

In the construction as described above, the substrate 16 on the top ofwhich the sample S is placed is attached to the XYZ stage 18, and whenthe XYZ stage 18 is driven in an arbitrary direction along the X-axisdirection, the Y-axis direction and the Z-axis direction and further theintermediate focus point A of the laser beam output from thetitanium-sapphire laser 12 by means of the condenser lens 14 isarbitrarily transferred to the Z-axis direction in the sample S,metallic structures M are fabricated on a locus of the above-describedintermediate focus point in a three-dimensional space.

EXAMPLE 1

FIG. 2 is an electron micrograph showing the results of fabricating asilver structure in the case where a AgNO₃ aqueous solution is used asthe sample S, and the sample S is relatively scanned with the laser beamoutput from the titanium-sapphire laser 12 at a scanning speed 50 μm/sby means of the above-described optical system 10 wherein anilluminating radiation power is 78.5 mW with respect to the sample S.

On one hand, FIG. 3 is an electron micrograph showing the results offabricating a silver structure in the case where a mixture prepared bydissolving Coumarin 440 into an ethanol solvent to a AgNO₃ aqueoussolution is used as the sample S, and the sample S is relatively scannedwith the laser beam output from the titanium-sapphire laser 12 at ascanning speed 50 μm/s by means of the above-described optical system 10wherein a concentration of Coumarin 440 is 0.02 wt % with respect to theethanol solvent, while an illuminating radiation power is 14.3 mW withrespect to the sample S.

The locus of the laser beam output from the titanium-sapphire laser 12is transferred so as to fabricate an inverted C-shaped silver structureoutside a C-shaped structure in both the experiments shown in FIGS. 2and 3.

As is apparent from the comparison of FIG. 2 with FIG. 3, it is foundthat sizes of both the silver structures are controlled at highprecision in the control of the exposure amount in the experimentalresults shown in FIG. 3, and further its spatial resolution isremarkably improved in spite of the fact that no strict control is madein the control of the exposure amount.

EXAMPLE 2

FIG. 4 is an optical micrograph showing the results of fabricating agold structure in the case where a HAuCl₄ aqueous solution is used asthe sample S, and the sample S is relatively scanned with the laser beamoutput from the titanium-sapphire laser 12 at a scanning speed 50 μm/sby means of the above-described optical system 10 wherein anilluminating radiation power is 142.9 mW with respect to the sample S.

On one hand, FIG. 5 is an optical micrograph showing the results offabricating a gold structure in the case where a mixture prepared bydissolving Coumarin 481 into a dimethylformamide solvent to a HAuCl₄aqueous solution is used as the sample S, and the sample S is relativelyscanned with the laser beam output from the titanium-sapphire laser 12at a scanning speed 50 μm/s by means of the above-described opticalsystem 10.

In this case, a concentration of Coumarin 481 is 0.1 wt % with respectto the dimethylformamide solvent, while an illuminating radiation poweris 39.3 mW with respect to the sample S.

The locus of the laser beam output from the titanium-sapphire laser 12is transferred so as to fabricate an inverted C-shaped gold structureoutside a C-shaped structure in both the experiments shown in FIGS. 4and 5.

As is apparent from the comparison of FIG. 4 with FIG. 5, it is foundthat sizes of both the gold structures are controlled at high precisionin the control of the exposure amount in the experimental results shownin FIG. 5, and further its spatial resolution is remarkably improved inspite of the fact that no strict control is made in the control of theexposure amount.

It is to be noted that a dye-sensitization method utilized in a photoconductor such as a photographic film which has been heretofore known isa method for intending primarily to increase an absorption sectionalarea of the photo conductor thereby improving sensitivity and specifyingwavelengths (cyan, magenta, yellow and the like layers in case of colorfilm).

On the other hand, the photoreduction method for metal complex ionsaccording to the present invention is quite different from aconventional dye-sensitization method in that changes in the absorptionspectrum of a material with exposure to light is reduced and an extentover which photoreduction effect due to the light irradiated locallyextends is limited in addition to that light absorption characteristicsof a material are allowed to change as described above, whereby spatialresolution of the metal structure may be improved. As a result, thefollowing functions and advantageous effects are obtained according tothe present invention.

(1) Changes in absorption wavelength and absorption sectional area dueto metal fine particles produced by exposure to light may be suppressedby adding a coloring matter.

(2) In the present invention, a femtosecond ultrashort pulse laser isused as a light source for taking place a photoreduction reaction, sothat the invention is particularly effective in a system wherein amultiphoton process is used for absorption. When such system asdescribed is applied, it becomes possible that an extent over whichinfluences of a laser beam being condensed at the intermediate focuspoint extend may be more spatially restricted, and as a result, ametallic structure may be fabricated in finer than a spot diameter of alaser beam decided by diffraction limit of a light.

(3) When a femtosecond ultrashort pulse laser is used as a light sourcethereby utilizing nonlinearity in a two-photon absorption process,spatial resolution can be given to an irradiation direction of the laserbeam, and as a result, a three-dimensional metallic structure can beeasily fabricated.

(4) Since a coloring matter may be selected suitably so as toaccommodate to a wavelength or a desired absorption wavelength of alight source, a tolerance in case of fabricating a metallic structurebecomes high.

(5) As a result of adding a coloring matter, energy conversionefficiency of a light source can be improved, and as a result, even whena laser beam is scanned at high speed, it becomes possible to produce ametallic structure, so that the throughput can be improved.

Furthermore, the above-described manner of practice and examples may bemodified as enumerated in the following paragraphs (1) through (4).

(1) In the above-described manner of practice and examples, although theinvention is described with respect to the case where a femtosecondultrashort pulse laser is used as a light source, it is not limited tothe femtosecond ultrashort pulse laser as a matter of course, but avariety of pulse lasers and continuous lasers are applicable.

(2) In the above-described manner of practice and examples, although avariety of coloring matters are shown, they are merely exemplifications,and the other coloring matters may also be used as a matter of course.

(3) In the above-described manner of practice and examples, although thegold ions and the silver ions are described for fabricating metallicstructures, the metal complex ions to which the present invention isapplicable are not limited to the gold ions and the silver ions as amatter of course, but the invention may be applied to a variety of metalcomplex ions.

(4) The above-described manner of practice may be suitably combined withthe modifications described in the above-described paragraphs (1)through (3), respectively.

It will be appreciated by those of ordinary skill in the art that thepresent invention can be embodied in other specific forms withoutdeparting from the spirit or essential characteristics thereof.

The presently disclosed embodiments are therefore considered in allrespects to be illustrative and not restrictive. The scope of theinvention is indicated by the appended claims rather than the foregoingdescription, and all changes that come within the meaning and range ofequivalents thereof are intended to be embraced therein.

The entire disclosure of Japanese Patent Application No. 2005-139329filed on May 12, 2005 including specification, claims, drawings andsummary are incorporated herein by reference in its entirety.

1. A photoreduction method for metal complex ions wherein a laser beamis beam-irradiated on a metal complex ion dispersion element dispersedin a material to photoreduce the metal complex ions thereby fabricatinga metallic structure, comprising: adding a predetermined coloring matterto the material in which the metal complex ion dispersion element isdispersed; and beam-irradiating the laser beam to the material to whichthe predetermined coloring matter has been added.
 2. The photoreductionmethod for metal complex ions as claimed in claim 1, wherein: thecoloring matter has the peak of absorption wavelength in the vicinity ofabout half of the wavelength of the laser beam which is beam-irradiatedto the material.
 3. The photoreduction method for metal complex ions asclaimed in claim 1, wherein: the functional groups of the coloringmatter have not a reducing ability with respect to the metal complex iondispersion element dispersed into the material.
 4. The photoreductionmethod for metal complex ions as claimed in claim 1, wherein: thematerial is Au⁺ aqueous solution; the coloring matter is any ofP-Quaterphenyl, Stilbene 420, Coumarin 440, Coumarin 481, Coumarin 485,Coumarin 500, or Coumarin 515; and a solution prepared by dissolving thecoloring matter into a dimethylformamide solvent is added to the Au⁺aqueous solution.
 5. The photoreduction method for metal complex ions asclaimed in claim 4, wherein: a concentration of the coloring matter is0.1 wt % with respect to the dimethylformamide solvent.
 6. Thephotoreduction method for metal complex ions as claimed in claim 1,wherein: the material is Ag⁺ aqueous solution; the coloring matter isany of Stilbene 420, Coumarin 440, Coumarin 504, or Coumarin 515; and asolution prepared by dissolving the coloring matter into an ethanolsolvent is added to the Ag⁺ aqueous solution.
 7. The photoreductionmethod for metal complex ions as claimed in claim 6, wherein: aconcentration of the coloring matter is set out at the amount ofsaturation with respect to the ethanol solvent.